The invention pertains to the field of nonlinear impedance transformers NIT which can be used to accept, with good impedance match, driving pulses from gallium arsenide FET's at any frequency from near D.C. to over 3 GHz and generate compressed fall time output pulses at any selected output impedance (preferably a value matched to the load circuit being driven by the NIT). These output pulses can be used to drive samplers for sampling very high frequency RF signals. The output pulses can also be used to drive trigger circuits or another nonlinear transmission line if further fall time compression is desired.
A difficulty with the integrated nonlinear transmission line defined in the parent cases for which the present invention is an improvement is that there were minimum driving frequency and minimum driving amplitude requirements which were difficult to meet. Basically, the minimum driving frequency for pulses from the local oscillator was 3 GHz. Further, a large amplitude was needed such that the slew rate of the local oscillator input signal was sufficient to be within an input window of slew rates or fall times which could be further compressed by the nonlinear transmission line. Such driving signals generally required travelling wave amplifiers or step recovery diodes to generate. Neither was convenient.
Further, there was generally an impedance mismatch between the output impedance of the local oscillator and the input impedance of the nonlinear transmission line. This is because the nonlinear transmission line was designed to have a characteristic impedance of preferably around 50 ohms to maximize the efficiency of injection of power into the sampling head. This characteristic impedance for the nonlinear transmission line generally did not well match the output impedance of the local oscillator. The result was inefficiency of power injection into the nonlinear transmission line. The output impedance of a more convenient FET type local oscillator driver is generally around 10 ohms.
Therefore, a need has arisen for a nonlinear transmission line type impedance transformer that can compress local oscillator pulse fall times as well as have an input impedance which matches the output impedance of an FET local oscillator and which has an output impedance which matches the input impedance of the sampler to maximize efficiency of power transfer and minimize reflections and ringing problems.
Also a need has arisen for a more compact integrated nonlinear transmission line structure. This structure must have a characteristic impedance which is high enough to yield an overall characteristic impedance of approximately 50 ohms output impedance when periodically loaded by a plurality of Schottky barrier varactor diodes.